GB2248276A

GB2248276A - Hydraulic actuating device

Info

Publication number: GB2248276A
Application number: GB9119851A
Authority: GB
Inventors: Manfred Kahrs; Gerhard Kunz; Franz Fleck; Gerhard Schudt
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1990-09-27
Filing date: 1991-09-17
Publication date: 1992-04-01
Anticipated expiration: 2011-09-17
Also published as: JPH04234583A; ITMI912114A1; GB2248276B; FR2667366A1; IT1251143B; US5201175A; ITMI912114A0; DE4030570A1; GB9119851D0

Abstract

A hydraulic actuating device comprising a pump (1) which, in operation, continuously supplies fluid out of a reservoir into a pressure line (22, 23). The device also comprises a pressure-limiting valve limiting the pressure in the pressure line (22, 23), and a control valve connected to said pressure line (22, 23) by which an operating cylinder is connectible to the pressure line (22, 23). An air chamber in communication with the pressure line (22, 23) is formed by a housing bore (26) in order to augment the regulating speed of the operating cylinder in the housing (10) of the pump (1), in which chamber an air volume is retained and displaces part of the pressure fluid volume required for actuation of the operating cylinder when it is relieved due to the system pressure determined by the pressure-limiting valve reducing to the operating pressure prevailing on pressurisation of the operating cylinder. The air chamber may be provided elsewhere in the pressure line. <IMAGE>

Description

1 HYDRAULIC ACTUATING DEVICE The present invention relates actuating

device.

to a hydraulic More specifically, the present invention relates to 5 a hydraulic actuating device of the type comprising a pump which, in operation, cohtinuously supplies fluid out of a reservoir into a pressure line, a pres sure- limiting valve limiting the pressure in the pressure line, a control valve connected to said pressure line, and an operating cylinder which is connectible to the pressure line via the control valve.

Actuating devices of this type are commonly known as, for example, from the journal lKonstruktion 121 (1960), volume 9, page 380, pictures 13 and 17. They are characterised by their simple structural design. However, a disadvantage with these actuating devices is that, in order to attain high regulating speeds, pumps with a correspondingly great displacement volume are required and such pumps in turn increase the structural complexity and the space requirement of the devices, and they augment the energy demand, which has to be considered as loss, in the periods of operation in which the control valve is closed and the delivery flow of the pump is discharged through the pressure-limiting valve.

Hydraulic actuating systems are also known from German published Patent Application 2324059 wherein the pump charges a pressure accumulator from which pressure fluid is 2 taken for application on the operating member. Such systems are relatively sophisticated because they necessitate a pressure accumulator with a gas chamber separated by a diaphragm or a piston, and usually an accumulator-charging 5 valve in addition.

It is an object of the present invention to increase the regulating speed of the operating cylinder of a hydraulic actuating device of the type described above beyond the extent predetermined by the delivery of the pump without the employment of conventional pressure accumulators.

According to the present invention there is provided a hydraulic actuating device comprising a pump which, in operation, continuously supplies fluid out of a reservoir into a pressure line, a pressure- limiting valve limiting the pressure in the pressure line, a control valve connected to said pressure line, and an operating cylinder which is connectible to the pressure line via the control valve, characterised in that the device is structurally designed so that an air volume is retained in the pressure line or in a chamber in communication with the pressure line and displaces part of the pressure fluid volume required for actuation of the operating cylinder when said air volume is relieved due to the system pressure determined by the pressure-limiting valve reducing to the operating pressure prevailing on pressurisation of the operating cylinder.

The present invention serves to utilise the difference in pressure between the system pressure and the operating pressure as well as the air which is entrained in hydraulic systems by foaming in the reservoir and by other effects of pressure fluid in the form of small bubbles in order to accomplish an accumulating effect which, in parallel to the delivery by the pump, delivers part of the filling capacity of the operating cylinder and thereby reduces the regulating time considerably. The structural design needed therefor is surprisingly simple to achieve since it is generally sufficient for carrying out the 3 invention to retain the necessary air volume by forming a small clearance volume in the housing of the pump or the control valve or within the pressure line. Instead of designing a special clearance volume, provision can be made according to another aspect of this invention to enlarge the line cross-section of the pressure line to such extent that the pressure fluid volume enclosed therein contains the necessary air volume.

When the quantity of air carried along in the pressure fluid flow is too small, the present invention provides in accordance with another aspect thereof for the pump to dispose of means furthering the intake of air. In order to avoid the development of undefined air locks in the actuating device, the pressure-limiting valve can be arranged according to another aspect of the present invention such that excess air is evacuated to the reservoir. Furthermore, it can be ensured according to this invention by suitably positioning the ports that air out of the operating cylinder is discharged to the reservoir in the unpressurised condition.

Actuating devices according to the invention are particularly applicable to operating cylinders with small cylinder volumes which may be suitably employed for performing regulating actions in automotive vehicles. it has proven to be favourable that the retained air volume amounts to approximately 20 to 50% of the volume absorption of the operating cylinder.

By way of example the present invention will now be described with reference to the accompanying drawing in which:

Figure 1 is a circuit diagram of a hydraulic actuating device according to the invention; and, Figure 2 is a cross-sectional view taken through a radial piston pump with a clearance volume connected to the pressure line.

The actuating device shown in Figure 1 comprises a pump 1 which pumps fluid out of a reservoir 2 into a 4 pressure line 4 leading to a control valve 3. The pressure in the pressure line 4 is limited to a maximum value termed system pressure by means of a pres sure- limiting valve 5. Connected to the electromagnetically operated control valve 3 is an operating cylinder 6 with a piston 8 which, by pressurisation, is movable in opposition to a compression spring 7. The pressure chamber 9 of the operating cylinder 6 can be connected through the control valve 3 to either the pressure line 4 or the unpressurised reservoir 2 (as shown).

When the pressure chamber 9 is connected to the pressure line 4, an operating pressure will adjust in both lines which is lower than the system pressure defined by the pressure-limiting valve 5.

Figure 2 illustrates the pump 1 of the device of 15 Figure 1 in crosssection. A radial piston pump housed in a pump housing 10 is provided with a longitudinal throughbore 11 and a succeeding cylindrical recess 12. A control pin 13 is secured in the longitudinal bore 11, for instance by being forced therein, and projects into the recess 12.

A rotor 14 is rotatably mounted on the control pin 13 in the recess 12, said rotor incorporating a number of radially aligned cylinder bores 15 in which pistons 16 are slidably mounted. The pistons 16 are supported with their radially outer ends on the inner surface of a stroke ring 17 which is eccentric relative to the control pin 13 and rotatably mounted in the recess 12 by means of a roller bearing. Two control slots 18,19 are provided in the control pin 13 and located in the plane of the cylinder bores 15 so that on rotation of the rotor 14 the slots.move into communication with the individual cylinder bores 15. The control slot 18 connects via a longitudinal channel 20 and a bore 21 with a suction port in the housing 1 lying outside of the drawing plane. A longitudinal channel 22 leads from the control slot 19 to an annular groove 23 which is in communication with a pressure port lying outside of the drawing plane and connecting to the pressure line 4. The rotor 14 is driven by a shaft 25 via a coupling 24. The shaft 25 may be the cam-shaft of an internal-combustion engine.

In the envisaged mounting positon of the pump 1, the annular groove 23 is connected at its peak to a radially upwardly extending housing bore 26 which is closed in pressure-tight manner from the outside of the pump by a screw plug 27. A clearance volume of defined magnitude is formed by the housing bore 26 into which, on operation of the pump 1, air which is carried along by the pressure fluid on its way from the longitudinal channel 22 to the annular groove 23 can ascend before the pressure fluid propagates through the annular groove 23 to the pressure port. This causes the housing bore 26 to gradually fill with air which is compressed by the comparatively high system pressure when the control valve 3 is closed. Once the control valve 3 is operated and the pressure line 4 is connected to the operating cylinder 6, the air enclosed in the housing bore 26 will expand due to the pressure in the pressure line 4 decreasing to the lower operating pressure and thereby displaces a pressure fluid volume which adds to the delivery flow of the pump 1. As a result, the pressure chamber 9 of the operating cylinder 6 will f ill up more quickly and a correspondingly shorter regulating time will be achieved. In practical tests a reduction of the regulating time of more than 30% could be achieved by the described measure.

The clearance volume formed by the housing bore 26 is suitably dimensioned to be of such size that it can receive the air compressed under system pressure during operation. When the air expands during the transition to the operating pressure by switching of the control valve 3, part of the air contained in the clearance volume will escape and finally will leave the system towards the reservoir 2 when the control valve 3 is switched back. This portion of air will be replaced again by the delivered airloaded pressure fluid after the end of the actuation during renewed build-up of the system pressure.

6

Claims

CLAIMS:

1. A hydraulic actuating device comprising a pump which, in operation, continuously supplies fluid out of a reservoir into a pressure line, a pres sure- limiting valve limiting the pressure in the pressure line, a control valve connected to said pressure line, and an operating cylinder which is connectible to the pressure line via the control valve, characterised int hat the device is structurally designed so that an air volume is retained in the pressure line (4) or in a chamber (26) in communication with the pressure line (4) and displaces part of the pressure fluid volume required for actuation of the operating cylinder (6) when said air volume is relieved due to the system pressure determined by the pres sure- limiting valve reducing to the operating pressure prevailing on pressurisation of the operating cylinder.

2. An actuating device as claimed in claim 1, characterised in that a clearance volume (26) for retaining an air volume is designed into the housing (10) of the pump (1) or the control valve (3) or within the pressure line (4).

3. An actuating device as claimed in claim 1 or 2, characterised in that the line cross-section of the pressure line (4) is enlarged to such extent that the pressure fluid volume enclosed therein contains the air volume.

4. An actuating device as claimed in any one of the preceding claims, charcterised in that the pump (1) disposes of means furthering the intake of air.

5. An actuating device as claimed in any one of the preceding claims, characterised in that the pressurelimiting valve (5) is arranged so that excess air is evacuated from the pressure line (4).

6. An actuating device as claimed in any one of the preceding claims, characterised in that the positioning of the port or a number of ports of the operating cylinder (6), air is discharged out of the operating cylinder to the reservoir (2) in the unpressurised condition.

7 7. An actuating device as claimed in any one of the preceding claims, characterised in that the retained air volume amounts to approximately 20% to 50% of the volume intake of the operating cylinder (6).

8. An actuating device substantially as hereinbefore described with reference to the accompanying drawing.